BOULDER, Colo. — In the wake of the success of the Cassini mission to Saturn, there is overwhelming support for dispatching a spacecraft to Jupiter’s moon, Europa — an ice-covered world that may support an ocean, possibly teeming with life. Another high-priority target is Titan, a moon of Saturn.

The ongoing Cassini mission that dropped off Europe’s Huygens lander has shown Titan to be an outlandish mini-world, deserving of further, intensive scrutiny. One "trial balloon" of a concept is to study Titan using a blimp-like vehicle that floats over the moon’s surface.

Leading space scientists gathered here to attend a June 9-10 meeting of NASA’s Outer Planets Assessment Group (OPAG), planning, prioritizing, and advocating a new exploration agenda for the distant planets.

"We need to understand the giant planets ... to find out how the solar system was made. The number one problem is how habitable planets are made," said Fran Bagenal, chair of the OPAG and a leading space scientist at the University of Colorado here in Boulder.

Bagenal said the exploration of the outer planets can provide knowledge about the stockpile of elements bound up in the giant planets, particularly Jupiter. Studying the processes involved in planetary formation can help discern what conditions played a role in shaping life on Earth and, perhaps, elsewhere.

"There are the exotic places that are cool and neat ... Titan and Europa ... that might be a successful place for life," Bagenal told SPACE.com.

Those taking part in the OPAG meeting are discussing a wide array of topics, such as an orbiter for Europa, a Titan orbiter and rover, a mission to Neptune, snagging bits of a far-flung comet for return to Earth, as well as new technologies for outer planet studies, such as an advanced breed of atmospheric probes.

OPAG was established by NASA in late 2004 to identify scientific priorities and pathways for exploration in the outer solar system. It solicits views from the scientific community and reports its findings to NASA Headquarters in Washington, D.C. While OPAG provides input to NASA, it does not make recommendations.

Slideshow: Best of Cassini
OPAG is evaluating outer solar system exploration goals, objectives, investigations and required measurements on the basis of the widest possible outreach into the scientific community.

Earlier this month, NASA announced a go-ahead on the Juno mission to conduct an in-depth study of Jupiter, the second mission in NASA’s New Frontiers Program. It is to be ready for launch no later than end of June 2010.

The first New Frontiers spacecraft — the nuclear-powered New Horizons mission to Pluto and the Kuiper Belt — is headed for a January 2006 departure. While the nuclear launch approval process still remains, the spacecraft itself is undergoing final testing for next year’s liftoff.

U.S./European collaboration
New NASA chief, Mike Griffin, has already backed in Senate testimony a Europa Orbiter. Accordingly, a team has been funded by NASA to take a quick look at the spacecraft needed, in terms of power, mass, travel time, and other items.

For planning purposes, this group is looking at launch dates for a Europa Orbiter in the 2012-2015 range, although the later dates are more likely in terms of funding, according to information distributed at the OPAG meeting.

In parallel with this work, a 10-person team of U.S. and European scientists is being tasked to scope out the requirements of such a mission and potential areas of collaboration. There is interest in shaping the Europa Orbiter mission as an international undertaking — patterned after the highly successful Cassini mission now orbiting Saturn.

Once underway, this study group would provide their findings in eight months time. At the moment, there is no official new start for the Europa Orbiter. However, NASA-internal talk now spotlights such a mission — including a version with a lander/impactor — as part of NASA’s fiscal year 2007 budget.

Jewels of JupiterAt the OPAG gathering here, there is support for a dedicated look at Europa, one of many moons circling Jupiter. A Europa Orbiter mission has been on start/stop status for many years.

Scientists are keen on resolving for sure "the ocean notion". That is, whether or not an ocean truly exists underneath Europa’s icy facade.

A top science goal of the Europa Orbiter would be to confirm or rule out the presence of a subsurface ocean on the moon. Additionally, an intensive study would be done of Europa’s icy crust, to scout out possible zones of liquid.

The spacecraft would also scan for organic and inorganic material on Europa — as related to its astrobiology potential and help set the stage for future exploration of the moon.

Thanks to the work of the Cassini spacecraft and Europe’s Huygens probe of Titan, this enigmatic moon also cries out for follow-up exploration. It has turned out to be an exotic, Earth-like world, but also exhibits bizarre differences.

Ralph Lorenz, a scientist with the Lunar and Planetary Laboratory at the University of Arizona in Tucson, is taking part in the OPAG meeting. He points out that Saturn’s Titan appears set to challenge even Mars as a priority target of exploration.

Slideshow: Titan images
Lorenz is an advocate for a Titan airborne platform. It would cover vast distances of Titan’s terrain, flying over possible lakes and seas of liquid methane and ethane. A new vista would be surveyed by the aerial platform every day. The airship would offer up, down, and side-looking sensing and carry out other research.

Under autonomous control, the robotic airship might even deploy sample devices, even mini-robots lowered by tether onto Titan, Lorenz speculated. This mission concept and others are detailed in a soon-to-be published paper in Advances in Space Research, he said.

"The outer planets program is an opportunity to look for life under the ice in the ocean of Europa. It’s a way to also look for, who knows, some unimaginable kind of life on Titan," said Jeff Moore, a space scientist at NASA’s Ames Research Center in Mountain View, California.

By exploring the outer planets and the moons of these distant worlds, Moore told SPACE.com, you are studying radically different places that we’re familiar with, such as Earth and Mars. "It’s the visit to the truly exotic," he said.

Bagenal, OPAG’s chair, said that getting missions to the outer planets, due to the long travel distances, takes time and technology.

"We have to be clever and use technology to ask the right questions", Bagenal said. "And we have to be patient. These missions take a long time ... but they pay off."